PMMA/MEH-PPV Photoluminescent Polymer Blend as a Long Time

Exposure Blue-light Dosimeter

José Roberto Tozoni, Alexandre Marletta,

Adryelle do Nascimento Arantes and Luana Rodrigues de Oliveira

Institute of Physics, Federal University of Uberlandia, P. O. Box 593, Uberlandia, 38400-902, Minas Gerais, Brazil

Keywords: Host/Guest, Polymer Blend, Poly(Methyl Methacrylate), Poly[2-Methoxy-5-(2-Ethylhexyloxy)-1,4-

Phenylenevinylene], Photoemission, Long Time Exposure Blue-light Dosimeter.

Abstract: In the present paper the photoemission intensity versus excitation exposure time of host/guest

photoluminescent polymer blend has been investigated. The polymer blend was composed by poly(methyl

methacrylate) (PMMA) as a host, and Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-

PPV) as a guest. The photoluminescent blend was characterized by optical absorbance and steady-state

photoluminescence spectroscopy. The PMMA/MEH-PPV blend film presented high homogeneity and high

photoemission intensity. Moreover, the PMMA/MEH-PPV blend film photodegradation in function of

sample exposure time to the blue-light excitation curve presented long biexponential time decay. These

results suggest that the PMMA/MEH-PPV blend film could be used as a long time exposure blue-light

dosimeter.

1 INTRODUCTION

Conjugated polymers have received great scientific

and technological attention due to its applications in

the areas of light-emitting, photovoltaic and sensors

devices (Yu, 1996, Hide, 1997, Leclerk, 2001, Silva,

2011, Ferreira, 2014). The biggest challenges in the

development of polymer conjugated devices are

increase the light emission efficiency and the life-

time (Leclerk, 2001, Yan, 1994, Atreya, 1999, Yu,

2000, Jorgensen, 2008, Palacios-Lindon, 2013). In

this system the macromolecular association is,

generally, an undesired process, which decreases the

efficiency of the light emission (Huser, 2001,

Tozoni, 2009, Spano, 2014, Chou, 2005, Mirzov,

2006, Lin, 2010).

Moreover, the conjugated polymer

photodegradation process cause changes in the

polymers structures and physical properties and has

lethal effects on efficiency of the devices (Silva,

2011, Ferreira, 2014, Yan, 1994, Atreya, 1999, Yu,

2000, Jorgensen, 2008, Palacios-Lindon, 2013). In

contrast, the alteration in the structural,

photoemission and the optical properties of solutions

and films of conjugated polymers, produced due the

photodegradation process, has been used in the

development of ionizing and non-ionizing radiation

dosimeters (Silva, 2011, Ferreira, 2014).

The photodegradation process is oxygen

dependent and has two possible pathways involving

the generation of either singlet oxygen or superoxide

radical anions (Atreya, 1999, Yu, 2000, Jorgensen,

2008, Palacios-Lindon, 2013, Soon, 2013).

Furthermore, dosimeters based in conjugated

polymers solutions, due the use of organic solvent,

are not safe for medical utilization. In addition, due

the macromolecular aggregation the films of

conjugated polymers have low photoemission

intensity and it is very difficult to obtain a structured

film using a small amount of conjugated polymers.

Other problem to use the conjugated polymers as

a long time irradiation exposure dosimeter is the fast

exponential time decay of the photoemission

intensity (Lee, 2011).

In a preceding paper, we have shown the de-

aggregation of the poly(9,9-di-hexylfluorenediyl

divinylene-alt-1,4-phenylenevinylene) (LaPPS16),

an electroluminescent polymer which shows a high

tendency to π-stacking aggregation, through the

formation of photoluminescent polymers blendes of

the LaPPS16 with several members of a series of

poly(n-alkyl methacrylate)s (Tozoni, 2009). The

PnMA/LaPPS16 blends present high mechanical

Tozoni J., Marletta A., Arantes A. and de Oliveira L.

PMMA/MEH-PPV Photoluminescent Polymer Blend as a Long Time Exposure Blue-light Dosimeter.

DOI: 10.5220/0006261403170322

In Proceedings of the 5th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2017), pages 317-322

ISBN: 978-989-758-223-3

317

properties and the photoluminescence spectra

presented high intensity and efficiency emission

(Tozoni, 2009).

Based on the above settings; in the fact of the

photodegradation process is oxygen dependent that

is dependent of the oxygen diffusion coefficient of

the polymers (Yu, 2000, Jorgensen, 2008, Shoee,

2015, Rothberg, 1996), in the fact that the PMMA

can works as a oxygen barrier (Yu, 2000, Jorgensen,

2008) and with the purpose to develop long time

blue-light dosimeters with greater light emission

efficiency, good mechanical properties and safer for

medical applications, in this paper was studied the

photodegradation of a photoluminescent polymer

blend composed by poly(methyl methacrylate)

(PMMA) as a host, and Poly[2-methoxy-5-(2-

ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)

as a guest. The results show that the PMMA/MEH-

PPV photoluminescent blend form a well structured

film with high homogeneity and high photoemission

intensity efficiency. Moreover, the PMMA/MEH-

PPV blend photodegradation curve presented long

biexponential time decay. These results suggest that

the PMMA/MEH-PPV blend could be used as a long

time blue-light dosimeter.

2 MATERIALS AND METHODS

The poly(methyl methacrylate) (Mw=350,000) was

purchased from Scientific Polymer Products Inc. and

was used as received. Poly[2-methoxy-5-(2-

ethylhexyloxy)-1,4-phenylene vinylene] (MEH-

PPV) and the chloroform was purchased from

Sigma-Aldrich, and was used as received too.

Solutions of PMMA/chloroform (262.5mg/15mL)

and PMMA/MEH-PPV/ chloroform

(262.5mg/0.216mg/15mL) and were prepared using

three sequential cycles of sonication (5 minutes) and

mechanically stirring (5 minutes) at 60

C. Then,

each solution were cast in one Petri dish at ambient

conditions and allowed to dry for a week, in the

dark. After the solvent evaporation the PMMA and

PMMA/MEH-PPV samples formed films with

thicknesses of about 100 m. Dried films of PMMA

and PMMA/MEH-PPV with dimensions of ~1.5x1.5

cm were separated for analyses.

AFM images were recorded using the Shimadzu

Scanning Probe Microscope (SPM-9600). Optical

absorption spectra were recorded using the

spectrophotometer FEMTO 800 XI. The steady-state

photoluminescence excitation (PLE) spectrum was

recorded on a Hitachi U-2001 spectrofluorometer.

The PMMA/MEH-PPV photoluminescence

emission spectra, over the entire band (500-800nm)

in function of exposure time to the blue-light

excitation and at ambient conditions, were obtained

by exciting the samples with a low-pressure mercury

vapour fluorescent lamp emitting light in the blue

part of the visible spectrum (Philips TL 20W/52

emission spectra over the entire band 400-540nm

with maxima at 450nm). This lamp is normally used

in incubators for the treatment of

Hyperbilirubinaemia in neonates. The

PMMA/MEH-PPV photoluminescence emission

spectra were acquired by Ocean Optics spectrometer

USB2000. The blend film was put at 38 cm apart the

lamp, the irradiance incident on the blend film

region was 5mW/cm

. Figure 1 shows the scheme of

the experimental setup.

Figure 1: Scheme of the experimental setup used for the

acquisition of the photoluminescence spectra versus time

of exposure to the blue-light excitation.

3 RESULTS AND DISCUSSION

Figure 2 shows the PMMA/MEH-PPV blend film

image after 45.50 hours of irradiation. Visually it is

observed that the sample presents great homogeneity

without presenting phase segregation.

Figure 2: PMMA/MEH-PPV blend image after 45.50

hours of irradiation exposure.

Moreover, due the reduction of absorption

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

318

(photobleaching in the central region), it is possible

to differentiate the irradiated region from the non-

irradiated region. Figure 3 shows the PMMA/MEH-

PPV blend film AFM images of the regions non-

irradiated and after 45.50 hours of irradiation

exposure.

Non-irradiated

Irradiated

Figure 3: PMMA/MEH-PPV blend AFM images before

and after 45.50 hours of irradiation exposure.

The AFM images show that the photo-oxidation

changes the blends morphology favoring the

formation of nanostructures

increasing the roughness

of the blend surface. Figure 4 shows the optical

absorbance spectra of the PMMA and

PMMA/MEH-PPV blend film in the UV-Vis range

and the Lamp Emission region (gray region).

Figure 4: Absorbance spectra of the cast film of PMMA

(open triangle), the PMMA/MEH-PPV blend film before

irradiation exposure (open circle) and PMMA/MEH-PPV

blend film after 45.50 hours of irradiation exposure (open

square). The gray inset figure shows the Lamp Emission

region.

The absorbance spectrum of PMMA shows that the

PMMA/MEH-PPV absorbance was independent of

the PMMA matrix. Furthermore, the absorbance

spectra of PMMA/MEH-PPV blend film are

broader, with maxima at ~542 nm before irradiation,

and ~517 nm after 45.50 hours o of irradiation

exposure. Figure 5 shows the normalized PLE

spectrum of the PMMA/MEH-PPV before

irradiation at wavelength detection of 590nm

(

Det

=590nm) and the normalized absorbance spectra

of the PMMA/MEH-PPV before and after 45.50

hours of irradiation exposure. These results show

that the absorbance spectra line shapes were

dependent of the film exposure time to the

excitation. After 45.50 hours of irradiation exposure

the PMMA/MEH-PPV blend film absorbance

spectrum was broadened, presents a significant blue-

shift (~25nm) and intensity decrease. The optical

absorbance spectrum modifications in function of

the film exposure time are due the photo-oxidation

that promotes changes in the chemical structure of

the PMMA/MEH-PPV blend film. These results

show that the photo-oxidation changes the

distribution of effective conjugation length to shorter

chains and increase the microscopic disorder (Yan,

1994, Rothberg, 1996, Atreya, 1999). The PLE

spectrum presents two maxima, one around ~566nm

(maximum of efficiency) and other around ~480nm.

37 5 45 0 525 600 675

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Absorbance ( 0.00 h)

Absorbance ( 45.50 h)

PLE (0. 0 0 h)

Normalized Intensity

Wavel ength (n m)

Figure 5: Normalized PLE spectrum of the PMMA/MEH-

PPV before irradiation exposure at wavelength detection

of 590nm (open star), the normalized absorbance spectra

of the PMMA/MEH-PPV blend film before irradiation

exposure (open circle) and after 45.50 hours of irradiation

exposure (open square).

The PLE spectrum maximum was red shifted

approximately 24 nm as compared to the optical

absorbance spectra. The difference between the

absorbance and PLE normalized spectra of the

PMMA/MEH-PPV blend (before irradiation)

suggests that, due the presence of aggregated

400 450 500 550 600 650 700 750 80

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Lamp

Emission

Region

PMMA

PMMA/MEHPPV (0.00 h)

PMMA/MEHPPV (45.50 h)

Absorbance

Wavelength (nm)

PMMA/MEH-PPV Photoluminescent Polymer Blend as a Long Time Exposure Blue-light Dosimeter

319

species, the exciton diffusion is very efficiently.

Due to the fact that MEH-PPV photo-oxidation

results in the creation of carbonyl groups that

quench the photoluminescence intensity (Rothberg,

1996; Yu, 2000; Jorgensen, 2008), and in order to

quantify and correlate this effect with the film

exposure time to the lamp light excitation measures

of the photoluminescence spectra of the

PMMA/MEH-PPV blend film in function of the

irradiation exposure time have been done. Figure 6

shows the PMMA/MEH-PPV blend film Integrated

PL intensity (over the entire band 580-800nm) in

function of sample time of exposure to the lamp

light excitation curve (0.00 to 45.50 hours in

intervals of 0.25 hours, open square) and the

biexponential fitting equation 1 (solid line).







+I



/



+I



/



(1)

The curve present a bi-exponential time decay

behavior with a long time t

= 16.67 hours and a fast

time t

=1.40 hours). Since the MEH-PPV photo-

oxidation depends on the oxygen diffusion in to the

sample (Yu, 2000, Jorgensen, 2008, Shoee, 2015,

Rothberg, 1996) and the PMMA can works at a

oxygen barrier (Yu, 2000, Jorgensen, 2008),

probably the fast decay time t

was due the photo-

oxidation of the superficial MEH-PPV and the long

decay time t

was due the bulk MEH-PPV photo-

oxidation.

Figure 6: PMMA/MEH-PPV blend film Integrated PL

intensity in function of the irradiation exposure time (open

square) and the bi-exponential fitting curve (solid line).

Figure 7 shows some PMMA/MEH-PPV blend film

PL spectra in function of sample irradiation

exposure time. The PL spectra present two well

defined maxima, one around ~600nm (0-0

transition) and other around ~640nm (0-1 transition).

Figure 8 shows some PMMA/MEH-PPV blend

film PL normalized spectra in function of sample

irradiation exposure time. No significant changes in

the MEH-PPV PL spectra line shapes were

observed, probably there was no formation of

aggregates and the PL intensity decrease is basically

due the carbonyl formations that work as a PL and

excitons quenchers (Atreya, 1999; Yu, 2000,

Jorgensen, 2008; Rothberg, 1996).

Figure 7: Various PMMA/MEH-PPV blend film PL

spectra in function of sample irradiation exposure time.

Figure 8: Some PMMA/MEH-PPV blend film PL

normalized spectra in function of sample irradiation

exposure time.

Moreover, like in the Rothberg et al. work the rapid

decrease of the PL intensity, while the absorption

decrease slowly, shows that the PL intensity is

extinguished by the photochemically induced defects

(Rothberg, 1996). Perhaps FT-IR experiments in

function of irradiation exposure time corroborate

this supposition.

0 5 10 15 20 25 30 35 40 45

Experiment

Fit Exponential (2 Decay)

Integrate

(

. u.

)

Exposure time (hours)

600 650 700 750

PM MA/MEHPPV P L Spectra

0.00

0.25

0.50

0.75

1.00

2.00

6.00

11. 00

16. 00

21. 00

26. 00

31. 00

36. 00

41. 00

Intensity (arb. u.)

Wavelength (nm)

600650700750

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00

1.00

2.00

16.00

26.00

PL Normalized Intensity

Wavelengt h (nm)

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

320

4 CONCLUSIONS

With the intention to develop long time irradiation

exposure blue-light dosimeters with greater light

emission efficiency, good mechanical properties and

safer for medical applications, in this paper was

studied the photodegradation of a photoluminescent

polymer blend composed by poly(methyl

methacrylate) (PMMA) as a host and Poly[2-

methoxy-5-(2-ethylhexyloxy)-1,4-

phenylenevinylene] (MEH-PPV) as a guest.

The results show that the PMMA/MEH-PPV

photoluminescent blend form a well structured film

with high homogeneity and high photoemission

intensity efficiency. Additionally, the PMMA/MEH-

PPV blend film photodegradation curve present a

biexponential time decay behavior with a long time

= 16.67 hours and a fast time t

=1.40 hours. These

results suggest that the PMMA/MEH-PPV blend

could be used as a long time irradiation exposure

blue-light dosimeter in the neonates treatment of

Hyperbilirubinaemia.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the support

from CNPq grant 307266/2013-3, CAPES,

FAPEMIG and INFIS-UFU. We are grateful to Prof.

Noelio Oliveira Dantas that allowed the use of the

spectrofluorimeter, and Guilherme de Lima

Fernandes by his assistance with the AFM images.

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